Botulinum toxin therapy for abductor spasmodic dysphonia

Area of Science:

• Laryngology
• Neuromuscular Disorders
• Pharmacology

Background:

• Botulinum toxin is effective for adductor spasmodic dysphonia (ADSD) but less so for abductor spasmodic dysphonia (ABSD).
• Potential reasons for poorer ABSD outcomes include differing pathophysiology and dose limitations due to posterior cricoarytenoid muscle (PCA) weakness.
• Asymmetric spasm severity is often observed in ABSD.

Purpose of the Study:

• To evaluate the efficacy of asymmetric botulinum toxin injections into the PCA muscles for treating ABSD.
• To establish a safe and effective dose escalation protocol for PCA botulinum toxin injections in ABSD patients.

Main Methods:

• An asymmetric dose escalation protocol was used for botulinum toxin injections into the PCA muscles.
• The nondominant PCA received a fixed dose (1.25 units).
• The dominant PCA dose started at 5 units and increased incrementally until symptom resolution, complete paralysis, or airway compromise was reached.

Main Results:

• Fourteen out of 17 patients achieved good or fair voice quality.
• Effective dominant-side doses ranged from 10 to 25 units.
• Two patients experienced exercise intolerance limiting PCA dose; one patient required medialization thyroplasty for persistent breathiness.

Conclusions:

• Asymmetric botulinum toxin injection into PCA muscles can successfully suppress abductor spasms in ABSD.
• Persistent breathiness may occur due to incomplete glottic closure, potentially requiring further intervention.
• This approach offers a viable treatment option for ABSD, with careful dose titration being key.